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1 Development of Frequency-Tunable Terahertz Radiation Sources Tsun-Hsu Chang 張存續 Department of Physics, National Tsing Hua University, Taiwan 2008 FISFES.

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Presentation on theme: "1 Development of Frequency-Tunable Terahertz Radiation Sources Tsun-Hsu Chang 張存續 Department of Physics, National Tsing Hua University, Taiwan 2008 FISFES."— Presentation transcript:

1 1 Development of Frequency-Tunable Terahertz Radiation Sources Tsun-Hsu Chang 張存續 Department of Physics, National Tsing Hua University, Taiwan 2008 FISFES Workshop November 6 – 8, NCKU, Tainan, Taiwan

2 2 Introduction:

3 3 Objective: Filling the Terahertz Gap R. Kleiner, “Filling the terahertz gap”, Science 318, 1254 (2007). Science, 23 November 2007

4 4 Terahertz Research THz photonics THz spectroscopy THz plasmonics Plasma diagnostics Fusion ESR DNP NMR Material processing Number of publications in Physical Review Letters. Search title/abstract using the key word--- “terahertz”.

5 5 Applications: high power ESR DNP NMR

6 6 How to Generate Terahertz Radiations Photonics: (low power, non-coherent) Josephson effect Quantum cascade laser Far infrared laser Femtosecond laser Electronics: (high power, coherent) Free electron laser Electron cyclotron maser - gyrotron Backward-Wave Oscillator Generate THz radiations:

7 7 Terahertz vacuum electron devices Terahertz FEL Generate THz radiations: high power FEL gyrotron BWO

8 8 高頻電磁實驗室 High Frequency Electrodynamics Laboratory 指導教授:朱國瑞老師,張存續老師 博士後:邱陳琦,姜惟元 博士班:高士翔,戴玲潔,吳家勳,吳光磊,陳乃慶,袁景濱 碩士班:林冠男,林柏年,康迺豪,劉煜,林柏宏, 姚仁傑,吳智遠,徐複樺,吳俊潭,姚欣佑 學士班:姜博瀚,郭彥廷,任德育,李育浚 校外合作:工研院材化所,中科院,同步輻射,高速電腦 國際合作: UC-Davis, USA, Fukui Univ., Japan Terahertz gyrotron term

9 9 Toward Bridging the Terahertz Gap one photon multiple-photon multiple photon per excitation, per electron, per electron, large interaction large interaction interaction space space space ~ wavelength    Frontier in science and technology. Terahertz gap

10 10 ECM based Devices --- gyrotrons gyro-monotron high average power gyro-BWO continuous frequency tunability (relatively unexploited) The gyrotron is a coherent radiation source based on the electron cyclotron maser (ECM) interaction

11 11 Difficulties for Terahertz gyro-BWO

12 12 Difficulties: Underlying Physics 2000 Nonlinear field contraction 2001 Nonstationary and chaotic behavior 2002 Linear and time-dependent behavior of gyro-BWO 2005 Dynamics of mode competition All published in PRL.

13 13 The high efficiency gyro-BWO T. H. Chang, C. T. Fan, K. F. Pao, K. R. Chu, and S. H. Chen, “Stability and tunability of Gyrotron Backward-Wave Oscillator”, Appl. Phys. Lett. 90, (2007).

14 14 Outer electrode Electron emitter Anode Vacuum container Center electrode (Cathode nose) 14 W-band TE A, A, 40.4 kG Difficulty #1: 110 GHz PNA Difficult #3: Electron gun Difficulty #4: Magnet Difficulty #2: THz mode converter T. H. Chang, et al., “W-band TE01 gyrotron backward-wave oscillator with distributed loss”, Phys. Plasmas 15, (2008).

15 15 First difficulty: Basic diagnostic system 2006: vector network analyzer E8363B 2,800,000 NTD. 2007: test set controller N5260A 2,400,000 NTD. 2008: Millimeter wave head module N5260AW10 2,600,000 NTD. Solved

16 16 Second difficulty: TE 01 mode converter 22 GHz Solved

17 17 Second difficulty  a main vantage T. H. Chang, C. H. Li, C. N. Wu, and C. F. Yu, “Exciting circular TEmn modes at low terahertz region”, Appl. Phys. Lett. 93, (2008).

18 18 Terahertz Devices Using LIGA Require high precision machining (<2 um)  LIGA technique 1. irradiation (mask) 2. development (SU-8) 3. electroforming 200 GHz TE 02 mode converter (for Fukui University, Japan) 400 GHz TE 41 mode converter (Fourth harmonic gyrotron) 4. cold test

19 19 Scaled experiment: Ka-band TE 01 gyro-BWO Distributed loss suppresses the axial-mode competition. Mode-selective circuit suppresses the transverse-mode competition. Tuning range: 15.8% Peak efficiency: 23.7%

20 20 Problem for gyro-BWO Old design (for gyro-TWT) Third difficulty: Electron gun Magnetron Injection Gun (MIG) for W-band gyro-BWO. CUSP gun for high harmonic gyro-BWO. New design (for gyro-BWO) W-band MIG gun is ready for fabrication. CUSP gun simulation

21 21 Fourth difficulty: Magnet Superconducting magnet (8 Tesla, 6,000,000 NTD) Pulsed magnet (40 Tesla, 3,000,000 NTD) Our old magnet is aging and has hysteresis effect. 2 Tesla is barely okay. Magnet is the biggest problem to us. Sufficient research funding can solve the problem.

22 22 Reducing the Magnetic Field Requirement Second harmonic slotted gyro-BWO: N. C. Chen, C. F. Yu, and T. H. Chang, “A TE21 second-harmonic gyrotron backward- wave oscillator with slotted structure”, Phys. Plasmas, 14, (2007).

23 23 Gyrotrons at Fukui FIR Center 0.4 THz, 1.5 kW 1 THz 0.25 kW A series of LHe free superconducting magnets: 8T, 12 T, 17 T, and 21 T.

24 24 International Cooperation: 394 GHz Frequency tunable gyrotron

25 25 International Cooperation: 203 GHz TE 02 gyro-BWO Novel TE 02 mode converter using LIGA technique. Novel mode-selective circuit

26 26 Conclusion and Foresight Terahertz gap NTHU Terahertz Research Center


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